For example, girders and columns of a building have concrete reinforcements embedded in concrete, including steel frameworks having main reinforcements wound with additional reinforcements for shearing such as hoops, stirrups and spiral hoops.
These steel reinforcements are widely used for various concrete constructions since their cost is relatively small and they have sufficient strength. With recent progress in architecture and civil engineering, there are, however, the following problems to be solved:
(1) It is difficult to provide large-sized reinforcing units since they are poor in transportability and workability on the construction site due to their considerable weight;
(2) Binding, welding and pressure welding of steel reinforcements are rather laborious and thus take a considerable part of the cohstruction period for concrete construction;
(3) It is very hard to enhance accuracy in assembling steel reinforcements since the bending of large diameter reinforcement bars is difficult on the construction site;
(4) Steel reinforcements necessitate control for preventing corrosion during storage and are further liable to cause breaking away of the concrete due to corrosion thereof; and
(5) Considerable differences in the covering depth of concrete between the main reinforcements and reinforcements for shearing occur in columns and girders of concrete construction such as a building, since main reinforcements and reinforcements for shearing are embedded in the concrete in a crosswise manner to form different levels between them.